Mass spectrometers



April 17, 1962 J. BISHOP ETAL MASS SPECTROMETERS Filed Jan. 30, 1957 United States Patent 3,030,505 MASS SPECTROMETERS John Bishop, Bebington, Wirral, and Paul Bernard Francis Evans, Saughall, Win'al, Cheshire, England, assignors to The United Kingdom Atomic Energy Authority, London, England Filed Jan. 30, 1957, Ser. No. 637,255 Claims priority, application Great Britain Jan. 31, 1956 2 Claims. (Cl. 250-41.9)

This invention relates to mass spectrometers and it is concerned principally with mass spectrometers for the analysis of materials in the solid state.

Solid material mass spectrometry gives rise to certain problems not encountered in gaseous analysis. The primary problem is that of treating the solid material so as to produce a steady source of ions without any mass discriminations. Secondary problems arise such as the avoidance of memory effects (which are errors due to contamination of the ion chamber by the previous sample) and the method of feeding samples to the ion chamber.

In normal operation, an ion source has to be removed from its associated analysis tube after every sample and thoroughly cleaned to reduce memory efiects before any new sample can be loaded. An essential part of the cleaning process is the heating of the ion source in the mass spectrometer until the residual ion beams are too small to interfere with the succeeding sample. The source is then removed, loaded with the sample and reinserted in the instrument. The sampling rate is the total time taken for one complete cycle of operations, much of this time being spent evacuating and admitting air to the spectrometer and obtaining stable ion beams. For a single simple mass spectrometer the minimum time in which this series of operations can be done is 4 hours. A faster rate of sampling requires additional spectrometers.

Schemes have been proposed for feeding samples to the ion chamber so that the vacuum does not have to be destroyed and built up again after each sample. Such known schemes give rise to mechanical complexities and operating difficulties which, in the absence of very skilled operators, prevent any substantial improvement in the sample rate.

The present invention sets forth mass spectrometer apparatus which provides for a more speedy analysis of samples than that possible with conventional apparatus and which is relatively simple to operate.

The mass spectrometer according to the invention comprises pairs of ion sources each associated with a collector system and means for controlling the direction of the analysing magnetic field so that the. ion beams from the sources can be individually selected for collection at their associated collector.

In the simplest arrangement the spectrometer anlyse'r is made in the form of three tubes so as to be Y-shaped. The tubes are spaced from each other by 120 (i.e. beam deflection ange of 60), one carrying the collector system and the other two each carrying an ion source. The necessary uniform analysing magnetic field is supplied by an electromagnet centred over the confluence of the tubes and means are provided for reversing the field so that ion beams from one or other of the sources are selected for analysis.

A further feature of the invention is the insertion of a simple flap valve in between each of the sources and the main analyser thus permitting easy removal of the ion sources without interfering with the main vacuum system.

The invention will now be further described with reference to the accompanying drawings wherein:

FIG. 1 shows diagrammatically a plan view of a spectrometer embodying the invention.

FIG. 2 shows a part sectional plan view.

Referring to FIG. 1 the analysis chamber comprises a Y-shaped tubular body part 10 having at the end of one of which is given by the points 28, 29, 30. Vacuum lines 18, 19 are connected to a high vacuum pump and lines 20, 21 are connected to a rotary pump through valves 22, 23. Between the ion sources 12, 13 and the analysis chamber 10 there are flap valves 24,25. In this apparatus the usual focussing criterion is achieved when the point source of the ion beam 26, the apex of the magnetic field 28, and the collector slit 31 are colinear: similarly for points 27, 29, 31. Lines joining points 26, 27, 31 are included to emphasize how the instrument is symmetrically disposed.

In the operation of this apparatus ion source 12 carries a sample whilst source 14 is being decontaminated. When the measurement of the sample in source 12 is completed, the magnetic field of electromagnet 17 is re- I Valves 22, 23 are opened to evacuate the valve chambers,

the flap valves 24, 25 being subsequently opened for the next cycle of operations. The combination of simultaneous operation of both sources and the use of the flap valve enables one sample per hour to be measured.

Referring now to the more detailed arrangement of FIG. 2 (using identical reference numerals to those used in FIG. 1 where practical for identification purposes). The analysis chamber 10 is shown in section and is provided with flanges 35, 36, 37. To the flange 35 the valve block ll and the ion source 12 are connected; similarly to flange 36 the valve block 13 and the ion source 14 are connected. To flange 37 the limb 15 and the collector assembly 16 are connected. The connections are made by bolts 33 and sealing is effected by rings 34. In the valve body are high vacuum pumping ports 18, 19 immediately behind the valve seat member 39 and flap member 4%) and pumping ports 29, 21 in front of the sources 12, 14. The flap member 40 has a rubber sealing disk 41 which is held in position with screw and washer 42. The flap member 40 is pivotted on. a pin 43 in a forked arm 44. The arm 44 is carried on a spindle 45 having one bearing 46 in the valve block 13 and the other bearing in a bush 47 located on a flange 59 supported by bolts 60, and sealed by a ring 61. (In order to describe the construction of this valve fully, the part enclosed in box 38 is a section at a lower plane than that of the principal section of FIG. 2.) The bush 47 is surmounted by sealing rings 50 and a compression bush 51 which is compressed on to rings 50 by bolts 49. The spindle 45 has a square head 52 on which is fixed a lever 53 by screw and Washer 54. Now referring to the valve numbered 24, the lever 53 has a tightening bar 55 held by a pin 56. The bar 55 passes through a slotted lug 58 and has a wing-nut and washer 57 that can be tightened against the lug so as to close the valve flap 40 tightly on the seat 39. When open, the flap member 40 is removed completely out of the path of the ion beam from source 14. The ion sources 12, 14-, are not shown in great demembers 64, '65. The members forming the rectangle" are bolted together by bolts 66". The pole pieces, which are not fastened in any way to the core of the electromagnet, are of triangular form 48, with the apexes cut away for convenience of mounting on three supports 67 which-are adjustable horizontally by screws 68 and vertically by screws 69. The screws 68 are threaded into brackets 70 held to the frame by screws 71. The ends of the screws 68 press against brackets 72 movable with the screws 69. Screws 73 associate the brackets 72 with supports 67.

The operation of the apparatus of FIG. 2 follows clearly from the description made with reference to FIG. 1.

We claim:

1. A mass spectrometer comprising an evacuable envelope, two ion sources and an associated collector system contained within said envelope, means for setting up an analysing magnetic field across said envelope and means for controlling the direction of the analysing magnetic field so that ion beams produced can be individually selected for collection atthe collector .system, said enve" lope being made in the form of three tubes so as to be Y-shaped, the collector system being contained in the foot of the Y and the ion sources being contained one in each arm of the Y. a a

2. A mass spectrometer according to claim 1 in which a valve is inserted between each of the ion sources and the confluence of the three tubes forming the evacuable envelope.

' No 'references cited; 

